1. Field of the Invention
This invention relates to oxidatively drying binders obtainable by the reaction of (A) (i) hydroxyl group-containing partial esters of polyhydric alcohols and long-chain unsaturated fatty acids and/or (ii) hydroxy group-containing alkyd resins of polyhydric alcohols, long-chain unsaturated fatty acids and polycarboxylic acids with (B) specific aromatic diisocyanates, to a process for the production of these binders and to their use for the production of coatings. The binders according to the invention are suitable for the production of high-body coating compositions which may be processed to form coatings having high resistance to water.
2. Description of the Prior Art
Oxidatively drying binders containing ester groups and urethane groups include alkyd resins wherein the polycarboxylic acid component has been completely or partly replaced by one or more polyisocyanate components (D. H. Solomon, The Chemistry of Organic Film Formers, John Wiley & Sons, New York 1974, 215). The modification of alkyd resins with polyisocyanates to improve their drying properties is known (Fette und Seifen 52 (1950), 20). In the case of saturated and unsaturated polyesters, this modification with isocyanates has been recommended with a view to obtaining greater hardness and better compatibility (DE-OS No. 19 15 800).
Although modification with isocyanates affords some advantages, it also gives properties which are not entirely satisfactory. These include above all inadequate body and tendencies towards hazing in unpigmented lacquer films and also moderate water resistance of the coatings obtained.
Accordingly, an object of the present invention is to provide oxidatively drying binders containing ester groups and urethane groups which do not have any of the above-mentioned disadvantages.
It has now surprisingly been found that phenylene diisocyanates substituted by long-chain hydrocarbon radicals lead to modified binders which satisfy the stated requirements to a high degree.